My online encyclopedia pegs the speed of light at about
300,000 km/s with which I'm in agreement with. The speed of light can't be exceeded in a perfect vacuum (but empty space doesn't exist due to QM) which I'm also in agreement with, theoretically speaking.

Now going back to the time of the Big Bang (a slight joke here since time didn't exist at the beginning), my understanding is the speed of light was different back then. If so, what was going on with light and how did it settle at its current constant and can it change in the future?